A near miss is an unplanned event that did not result in injury, illness, or damage - but had the potential to do so

The often misunderstood phrase is so-called to stress that not only had things gone remotely off course towards danger, but they had actually only "barely missed" catastrophe. For instance, commercial airliners are considered dangerously close if they are one mile apart. If they pass at a quarter mile apart or less, this is a "near miss" because they were extraordinarily near each other when they missed collision.